How often should I have the pads and rotors changed on my 2000 Nissan X-Terra? on 2000 Nissan Xterra

I just bought it in July 2010, so I have no service records. The brakes seem to work OK, then the other dy I needed to avoid a cat crossing the road and when I slammed on the brakes, the went "squishy", but worked. Just not as fst as I would have thought they would. The service manul says to ignore the ABS light, because it will go off and on all the time, which mine does. In december the mechanic who changed my oil told me I needed to rbing it in to have the brakes worked on. How can I know when to do this? Thanks in advance for your prompt response...